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Volume 13, Number 12—December 2007

Research

Swine Workers and Swine Influenza Virus Infections

Gregory C. Gray*Comments to Author , Troy McCarthy*, Ana W. Capuano*, Sharon F. Setterquist*, Christopher W. Olsen†, Michael C. Alavanja‡, and Charles F. Lynch*
Author affiliations: *University of Iowa College of Public Health, Iowa City, Iowa, USA; †University of Wisconsin-Madison School of Veterinary Medicine, Madison, Wisconsin, USA; ‡National Cancer Institute, Bethesda, Maryland, USA;

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Table 2

Odds ratios for elevated hemagglutination inhibition assay antibodies (enrollment sera) against swine influenza virus using proportional odds modeling*

Variables n Swine (H1N1)
Swine (H1N2)
Unadjusted OR 
(95% CI) Adjusted OR†
(95% CI) Unadjusted OR 
(95% CI) Adjusted OR† 
(95% CI)
AHS swine-exposed 707 35.8 (8.7–146.8) 54.9 (13.0–232.6) 17.2 (7.9–37.7) 13.5 (6.1-29.7)
AHS nonswine-exposed 80 10.6 (2.4–47.5) 28.2 (6.1–130.1) 4.7 (1.9–11.4) 6.9 (2.8-17.2)
University controls 79 Ref Ref Ref Ref
Age continuous
866
1.00 (0.99–1.01)
0.97 (0.96–0.98)

1.02 (1.01–1.03)

Sex
Male 484 3.7 (2.8–4.9) 3.3 (2.4–4.5) 3.5 (2.7–4.5) 3.0 (2.3-4.0)
Female
382
Ref
Ref

Ref
Ref
Received flu shot in the past 4 y
Yes 479 1.0 (0.8–1.3) 1.4 (1.1–1.9) 1.3 (1.0–1.7)
No/unsure
387
Ref
Ref

Ref

Human influenza (H1N1) (titer >40)
Positive 347 1.1 (0.9–1.4) 1.6 (1.2–2.0) 1.8 (1.4-2.4)
Negative 519 Ref Ref Ref

*OR, odds ratio; CI, confidence interval; AHS, Agricultural Health Study; AHS swine-exposed, participants from the AHS who reported working in swine production; AHS nonswine-exposed, participants from the AHS who denied ever working in swine production, 94% were spouses of AHS swine-exposed; university controls, faculty, staff, and students from the University of Iowa who denied ever working in swine production.
†Final multivariable models were designed that used a saturated model including all potential risk factors (see Methods) and manual backwards elimination.

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